Slide 1 - Forces & Motion

Slide 2 - What is a force?

• A force is a push or a pull
• A force can be described by its strength and direction
• The units of force are the newton (N)
• Like velocity, we always specify a direction for a force.
• Ex. 28 N to the right or 14 N down

Slide 3 - Net Forces

• A net force is the combination of all the forces acting on an object.
• A non-zero net force will cause an object to move

Slide 4 - Example

• Two people are pushing on opposite sides of a box.
• The stronger person pushes with 20 N of force to the left
• The weaker person pushes with 15 N of force to the right
• What is the net force on the box?
• 15 N
• 20 N
• 5N
• The net force is 5 N to the left
• The box will move to the left

Slide 5 - Force due to Friction

• A force that two surfaces exert on each other when they are in contact and motion.
• The friction force acts in the opposite direction than the motion of the object
• Friction depends on the type of surfaces and how hard they surfaces are pushed together.

Slide 7 - Example of Friction

• You are pushing a box across the floor with 10N of force to the left.
• The force due to friction is 2N.
• What is the net force on the box?
• 2N
• 10N
• 8N
• The net force is 8N to the left.

Slide 8 - The Force due to Gravity

• Gravity is a force of attraction between two objects with mass
• The more mass an object has, the greater it’s gravitational attraction
• The closer an object is, the greater it’s gravitational attraction
• Gravity depends on the mass of the objects and their distance apart.

Slide 9 - Gravity on Earth

• On Earth, gravity always causes an object to accelerate at 9.8 m/s2
• So when objects fall towards Earth, each second they fall 9.8m/s faster than the second before.